There are two important voltage values in measuring a breakdown voltage of a semiconductor device. One is a voltage at which a device under test (DUT) presents a breakdown phenomenon when the voltage applied to the DUT is increased. This voltage is called a breakdown trigger voltage, and is hereafter referred to as a trigger voltage. The second is a voltage at which a breakdown phenomenon is ceases, that is, breakdown current is zero at this time, when the voltage applied to the DUT is gradually lowered. This voltage is called a breakdown latchback voltage, and is hereafter referred to as a latchback voltage.
Conventionally, a measuring circuit having a composition as shown in FIG. 3 (a) has been used for measuring such trigger voltage and latchback voltage. The measurement is taken in such a manner that pulse signal is applied to a DUT 101 by a pulse generator 301 and the current flowing in the DUT 101 is connected through a current probe 302 and the voltage Vd between terminals of the DUT 101 is connected directly to respective channel inputs of an oscilloscope 303, thus observing waveforms. FIG. 3 (b) shows these measured waveforms. It is understood that the trigger voltage and the latchback voltage are measured, respectively.
However, there are some drawbacks in this measuring method. First of all, a large current is applied to the DUT at the time of breakdown phenomenon and there is a fear that the DUT is destroyed because of thermal and electrical stresses. In particular, as individual semiconductor elements become smaller, they are more susceptible to thermal and electrical stresses. Also, the temperature of the DUT itself rises due to heat generated by the electrical current, and characteristic change of the DUT is induced, thus making it impossible to take an accurate measurement. Furthermore, a high speed waveform observation in the order of 0.1 sec is microsecond is required for observing such a breakdown phenomenon, which makes the measuring system expensive.